Fluid coking of heavy hydrocarbons



R. w. PFEIFFER ETAL 30 FLUID coxmc OF HEAVY HYDROCARBONS April 7, 1959Fil ed. Aug. 19, 1953 3 Sheets-Sheet 1 BURNER VESSEL QUENCH) COOLER 6 I8 I 4 5 0 5 6 V l G 6 W 6 I MN 6 :6 A. a. N0 WN mn m a Tc BT W5 K 4 CE CKS 6 3 6 As RE OE I R 9 7 CS 9 V L 2 4 m .2 0 4 H x 1.... Hu X 1 v 2PLUM-Q1 1/ .3 M| |l|- Jk v G a 2 Z w 5 5 3 M 1 w. Iv Wm W 43 I 49FIGURE-I 68 6 Robert W Pfeiffer Daniel S. Borey Inventors Charles E.Jahmg By MAHorney April 7, 1959 R. w. PFEIFFER ET AL FLUID COKING OFHEAVY HYDROCARBONS 3 Sheets-Sheet 3 I- E a w m. a w E m 5 A U LG P, F mw mfm w w w W R H LE "n s VL/-\ 2 7/4 a u s s v W: 9 M- 4 x l R U .m m,5 M 4 F R 6 9 w M 7 a H I COKING VESSEL Robert W Pfeiffer Daniel S.Borey Inventors Charles' E. Jahnig e r 2,881,130 lQg Patented Apr-'1959' FLUID 'COKING F HEAVY HYDROCARBONS Robert W. Pfeilfer, Bronxville,N.Y., and Daniel S. Borey,

Crauford, and Charles E. Jahnig, Red Bank, N.J., assignors to EssoResearch and Engineering Company, a corporation of Delaware ApplicationAugust 19, 1953, Serial No. 375,088

4 Claims. (Cl. 208-127) This invention relates to coking of heavypetroleum residiums in contact with hot fluidized solids and to anapparatus particularly adapted for such coking.

The ever growing demand for high quality motor fuel makes itincreasingly imperative to upgrade heavy petroleum residues intodistillate stock, and notably into gas oil suitable for catalyticcracking into motor fuel of high quality. One method of producinggasoline from heavy residue commonly used for many years is to pass theoil through a heating coil where it is heated to incipient crackingtemperature and transfer it into a coking drum where it is maintaineduntil it is converted into vapors and coke. The operation is continueduntil the drum is substantially full of coke. Following this flow of hotoil into the drum is interrupted and after sufiicient coking is brokeninto lumps and removed. To make the operation continuous through thecoil a bank of coking drums may be provided for each coil so that theoil can be transferred from one drum to another as required. Thisprocess is commonly called delayed coking. The cooling down of thecoking drums and removal of the coke is a time consuming, laborious job.

More recently it has been proposed to coke these heavy residium oils byinjecting them into a coking vessel containing a fluidized bed of hotfinely divided solids and to supply the necessary heat by circulating astream of such solid through an external heater and back to the cokingvessel. This offers a great advantage over the delayed coking process inthat the operation is continuous. However, so far no commercial cokingunit of this type has been operated.

Development of this type of process has uncovered a number of problems.One particularly serious problem is the tendency of the bed to lose isfluidity or bog down. If this happens the Whole bed may solidify and itis then necessary to stop the operation, cool the coking vessel, breakup the coke into lumps and remove it from the vessel just as in thedelayed coking process.

Another serious problem is the building up of coke deposits in the vaporspace above the bed and in the line carrying the vapor effluent. Anotherproblem is the need to use relatively large amounts of extraneousfluidizing gas which dilutes the vapors leaving the vessel and increasesthe size and complexity of the subsequent fractionating and separatingequipment.

Another problem is to produce a gas oil suitable for catalytic crackingwhich is free of the metallic impurities such as nickel and vanadiumwhich has a poisoning effect on the cracking catalyst.

Another difficulty is proper control of the size of the particles. Asthe coke is formed on the particles of solid they continue to grow sothat unless some means are provided to supply fine particles, theparticles become bigger and bigger and will reach a point where thepatricles cannot be properly fluidized or circulated through the burner.

It is the object of this invention to provide an improved fluid cokingprocess and apparatus which successfully overcomes these and otherproblems. Other objects as well as the nature and advantages of theinvention will appear more clearly from the subsequent description,especially when read with reference to the accompanying drawing inwhich:

Fig. 1 is a simplified showing of the apparatus forming a part of thepresent invention and in which the process may be carried out;

Fig. 2 is an enlarged view of the upper separating and fractionatingsection of the coking vessel showing parts in section;

Fig. 3 is an enlarged detail of the feed injection nozzle, and

Fig. 4 illustrates a modification.

Referring to Figure 1, liquid feed passes into the coking system throughline 1. Feeds suitable for the present invention are heavy or reducedcrudes or vacuum bottoms or other heavy hydrocarbons containing asubstantial amount of constituents which cannot be vaporized withoutdecomposition. Typically, such feeds may have an API gravity of about 0to 20, e.g., 1.9", and a Conradson carbon content of about 5 to 40weight percent, e.g., 30%. This feed is preferably preheated byconventional means to about 400 to 750 F., e.g., 700 F., so as to keepits viscosity reasonably low and to reduce the heat load on: the cokingunit. From feed line 1 the liquid feed may be introduced into the denseturbulent fluidized coke bed 2 located in coking vessel 3. To avoid thepossibility of the bed losing fluidity and bogging down, it is importantthat the feed be quickly and uniformly distributed over the individualparticles of the bed. While the highly turbulent fluid nature of the bedcauses rapid dispersion of the feed throughout the bed, it is best notto rely entirely on the turbulence of the bed to effect the feeddispersion. order to prevent wetting of the coke particles at the pointof feed injection and thus incur the risk of bogging the bed, the feedis preferably injected into the bed at a multiplicity of points bothcircumferentially and vertically. As shown the feed passes through amanifold line 4 hav-v ing branch lines 5 communicating with nozzles 6(see Figure 3). Any type of nozzle which will obtain a fine dispersionof the feed without requiring excessive amounts of dispersion gas may beused. One particularly good nozzle for this service is the jet typeillustrated in Figure 3 in which feed is fed into the nozzle inadmixture with dispersion steam through a central conduit having a port8. The conduit is surrounded by an annular passage 9 through whichpurging steam is passed to keep this zone free of coke and permitremoval of the nozzle. The steam oil mixture at the nozzle tip maycomprise from 25 to volume percent steam. It is generally possible tofeed between 350-450 barrels of oil per nozzle per day. These nozzlesare preferably of retractable type which permits the core to be removedand cleaned if they become The coke particles within the bed aremaintainedin.

a turbulent fluidized condition by the gases and vapors rising upwardlytherethrough. These gases and vapors will include fluidizing andstripping gas and vapors and gases formed by coking of the feed. Gasesrising in the:

lower portion of the bed meet additional gases formed in the upperportion so that the volume of gas continuously. increases as it passesupwardly through the bed. The gas velocity in the lower part of the bedmust be ade quate to maintain fluidization and effect the desiredstrip-. ping. By flaring the walls outwardly in the zone of feed 3injection, the increase in volume of gases resulting from vaporizationis more or less compensated for by increase in vessel diameter so thatthe velocity of the gases are maintained more or less uniform throughoutthe depth of the bed although there may be some increase in velocitytoward the top of the bed.

The average superficial velocity of the rising gases is preferablymaintained between .5 and 5 feet per second and preferably between 1 and3 feet per second depending upon the size of the particles making up thebed. Higher velocities will increase turbulence but will reduce beddensity.

.As before mentioned the individual particles making up the bed tend togrow as the operation proceeds and it is necessary to maintain controlover the size of the particles. It is preferred to operate with solidshaving an average particle size ranging between 75 and 500 microns indiameter with a preferred average particle size range between 150 and300 microns. Preferably not more than 5% has a particle size above 500microns while particles smaller than 40 microns tend to agglomerate orare swept out of the system with the gases. It is usually desirable tohave from 5 to 20% of particles between 40 and 125 microns to improvefluidization and to scour the intermediate portion of the equipment aslater described. While smaller particles provide more surface area,extremely fine particle are subject to agglomeration and otherdifficulties.

The coking zone is maintained at the desired coking temperature bycirculation of solids through a heater as later described.

The coking temperature may range from 850 to 1200" F. and preferablybetween 900 and 1100 F. Higher temperatures permit greater feed ratesand increase capacity but may tend to cause overcracking of the vaporswith resultant lowering of yield of desired distillate products.

The coking operation is usually carried out at relatively low pressure,such as from to 50 pounds per square inch gauge. While the process maybe operated under subatmospheric pressure, it is generally preferred tooperate at a vapor outlet pressure suflicient to force the vaporsthrough subsequent fractionating and separating equipment. To this endthe outlet pressure may be between and 25 pounds per square inch gaugeand usually between 5 and 15 pounds. The pressure in the lower portionof the vessel will be somewhat higher due to the hydrostatic headdeveloped by the fluidized bed.

As before stated, the lower portion of the coking bed below the point offeed injection serves as a stripping zone. Steam or other'stripping gasis injected into this zone through line 11 to displace hydrocarbonvaporsfrom the coke before removal of the latter from the coking zone.By locating the stripping zone in the bottom of the reactor the excessstripping steam displaces hydrocarbons rising upwardly through thecoking zone and aids in maintaining the desired turbulence and fluidityin that section. The stripper velocity may be between 0.3 and 5 ft. persecond. The stripping steam may be injected into the vessel throughnozzles at high velocity to cause attrition or grinding of the largerparticles to maintain the desired particle size. To this end the gas maybe injected at jet velocities of about 200-3000 ft. per second.

The-total amount of steam injected into the coking and strippingzonesmayequal about5 to 3 0 weightpercent of liquid hydrocarbon feed, 6 to 15percent being the normal range.

If desired, disc and doughnut baffles may be located in the strippingzone to improve contact between the steam and solids. As mentionedbefore, the liquid bydrocarbon feed is injected into the reactorvthroughnozzles -6 at various levels and is-evenly deposited on thecokeparticles constituting the dense turbulent fluidbed. The-hydrocarbonfeedrate maybeabout 0,1 tofl3 weight ,4 per hour per weight of solidspresent in the fluid bed depending upon the composition of the feed,coking temperature, residence time of.- solids in the bed and otherfactors. The limiting factor is the ability to maintain the bed in ahighly turbulent fluidized state. If the feed rate is too high the solidparticles tend to stick together forming larger agglomerates and unlesscare is taken the whole bed may solidify and lose its fluidcharacteristics. This should be avoided or the process becomesinoperable and the plant must be shut down and the solidified bedremoved from the coking vessel.

In the fluid bed the feed is converted to solid coke and hot hydrocarbonvapor. The vapors leaving the bed carry entrained solids. To permit someof these solids to settle out of the vapors, it is usually best tomaintain the bed level 12 a substantial distance below the top of thevessel. It is desirable to have a certain minimum amount of entrainedsolids in the disengaging space 13 above the level of the bed. The heatcontained in the entrained solids will help to maintain temperature inthis zone at a higher level and prevent condensation and coking ofhigher boiling vapor products. In addition the entrained solids willserve to scour the walls of the vessel of any coke which tends todeposit. It is also desirable to minimize the residence time of thevapors .in this zone to prevent further thermal cracking. To this end,the cross section of vessel 10 above the fluid bed level 12 may bereduced so as to increase the velocity of the rising vapors in thedisengaging zone 13. This increased velocity entrains more coke, reducesvapor residence time, and keeps the reactor walls hotter and sominimizes condensation and coking as well as thermal cracking. Thevelocity of the gases in the disengaging zone maybe between 2 and 5 feetper second depending on particle size and other factors. If desired,additional hot coke may be introduced into the disengaging space aslater described. The vapors pass from the top ofthe disengaging zoneinto dust separating devices such'as cyclones 14 which serve to separateentrained coke particles from the vapors. The separated fines arereturned to the bed through dip legs 15.

Aeration gas may be injected into the dip legs 15 through line 16 (seeFigure 2). The amount of aeration gas so introduced may be controlled toregulate the amount of solids separated by the cyclones. For example insome cases it may be desirable to maintain a certain minimum of solidsin the cyclone outlet to scour out any coke which may form. Byincreasing the amount of gas added to the dip legs, the amount of solidsseparated by the cyclones may be reduced. The cyclones themselvespreferably are set in a solid transverse partition 16 which preventsvapors from reaching the stagnant zone above the cyclones and thusprevents coke from building up in this zone. From cyclones 14 the vaporspass through chimneys 17 into a scrubbing and fractionating tower 18mounted directly above the coking vessel.

The chimneys 17 preferably discharge the hot hydrocarbon-vapors againstheated baffles 19. The bafiles 19 are positioned a substantial distanceabove the bottom of the scrubbing tower 18 and the spacebelow thesebaffles forms a collecting zone for heavy condensate formed in thescrubber. This prevents the heavy condensate from falling back into thechimneys and building upcoke deposits therein.

' Chimneys 17, baffles 18 and all other walls separating the cokingvessel 3 from the scrubber tower 18 are preferably heavily insulated tominimize condensation and coking of the hydrocarbon vapors in thechimneys and bottom section-of the scrubbing tower. Heating elementspreferably may be provided around the walls of chimneys 17 and thecyclone outlet lines to keep the walls-hotter than the vapors asafurther aid in preventing undesirable qqndenss q and q k e h heating eem t a be in the form pf superheated steam coils jacketingthe Walls asshown. This heating steam may be preheated by indirect heat exchangewith hot solids in a later described coke burner and may be exhausted tothe atmosphere, so as not to further dilute the vapors passing tosubsequent fractionating and condensing equipment. Alternatively, hotflue gas from the coke burner may be used instead of steam in theheating coils. superheated steam may be injected directly into the hotvapors to minimize coking.

The temperature in the bottom of the tower 18 is controlled to condensethe heaviest portions of the vapors which contain metallic impuritiessuch as iron, nickel and vanadium compounds originally present in thefeed and carried overhead with the vapors. It will contain any entrainedsolids carried through the cyclones.

The temperature at the bottom of the tower 18 is controlled byintroducing a stream of quench oil through line 21. For example,condensate collected in the bottom of the tower may be removed throughline 24, a portion passed through cooler 26 (see Figure 1) and returnedto the tower above a series of disc and doughnut baffies 27. A portionof this recycle stream may be passed into the bottom of the towerthrough line 28 to further cool the products being withdrawn. Themaximum temperature at the bottom of the tower should not exceed about750 F. in order to prevent coking of this section of the equipment.

The temperature necessary to condense the metallic impurities willdepend on the nature and amount of such impurities present in the feed.For most feeds the final boiling point of the products leaving thebottom section will be between 950 and 1050 F. Since the productsleaving the scrubbing tower are composed of a wide mixture of vapors andgas, the end point of the uncondensed vapors will be considerably abovethe temperature maintained in the tower.

Vapors remaining uncondensed in the bottom scrubbing section of thetower pass upwardly through a series of bubble cap trays located in thetop of the tower where they are subjected to fractionation to condensean additional fraction of the gas oil boiling range. The condensateformed in the upper section collects in a trapout tray 29 and iswithdrawn as a side stream through line 31. A portion of this stream ispumped back to the lower section of the tower below the trap-out traythrough line 32 as additional scrubbing and cooling medium and anotherportion may be pumped through cooler 33 introduced into the top of thetower to serve as reflux.

The temperature at the top of tower 18 should be kept above the dewpoint of steam, i.e., at a temperature of at least 200 to 225 F. Thisprevents condensation of steam which, if allowed to occur, might causeemulsion and corrosion problems in the top of the tower. The temperatureof the vapors leaving the top of the tower may be about 300 F.

The heavy condensate fraction withdrawn from the bottom of the scrubbingtower 18, through line 24, and not recycled for quenching and scrubbingas before described may be pumped through line 34 back to the cokingvessel 3. The gas oil withdrawn as a side stream through line 31constitutes a final product of the process. This oil being a condensaterelatively free of residual components and metallic impurities may besubjected to catalytic cracking to form high quality gasoline.

Uncondensed vapors and gas are withdrawn from the top of tower 18through line 36, and passed through. water cooled condenser 37 (Figure2) and then to a separating drum 38 in which the liquid distillateseparates from uncondensed gas. The liquid will comprise the naphthafraction together with water. The naphtha is withdrawn .from theseparator through line 39. Condensed water may be withdrawn from drum 38through line 41. Wet gas may be withdrawn through line 42 and may berejected or further processed to recover desired products therefrornrInstead of further fraction- '6 ating the vapors from the scrubbingsection to segregate the gas oihnaphtha and gas as just described, thetotal vapors from the scrubbing zone may be passed directly withoutfurther fractionation to a catalytic cracking zone.

Returning to the coking vessel, a stream of solids is continuouslyremoved from the coking vessel through standpipe 43 which connects withthe vessel at a point spaced some distance above the bottom. The spacein the coking vessel below this line serves as a well or trap forcollecting any large lumps or agglomerates which might serve to plug thetransfer lines. The agglomerates may be periodically withdrawn throughconduit 50.

The standpipe 43 may have a wire cage or basket 44' around its inlet toprevent coarse lumps or agglomerates from lodging in the standpipe andconnecting lines and stopping flow.

The standpipe 43 connects at its lower end with a vertically inclinedconduit 45 which, in turn, connects with a vertical riser 46 having asection 47 projecting upwardly into the lower portion of the heatingvessel 48 below the level of a bed of fluidized solids maintainedtherein. To insure proper flow of solids from the coking vessel 3 to theburner vessel 48, care must be taken to maintain the solids aeratedthroughout their travel through these lines. The coke particles tend todeaerate very rapidly and it is necessary to add fluidizing gas atclosely spaced points 49 along the inclined pipe to prevent plugging ofthis pipe.

Additional carrier gas may be injected into the lower end of the riserpipe 46 through line 51 to control the density in this section of theequipment. If desired a part of the air for combustion may be injectedinto the riser.

The main stream of air for combustion is introduced through line 52 intoan auxiliary burner 53. Fuel for combustion is added to the auxiliaryburner through line 54. The auxiliary burner is normally used forheating up the unit at the start of the operation. After the unit isheated to proper temperature, the fuel supply is discontinued and theheat for the operation is obtained by burning coke formed in theprocess. In some locations, however, it may be more economical to burnextraneous gas rather than coke. In such cases the coke in the burnervessel 48 may be heated by combustion gases from the auxiliary burner.Gases, either air or hot combustion gases, as the case may be, pass fromthe auxiliary burner 53 into the bottom of the main burner vessel 48.The outlet from the burner is provided with a hood 55 to prevent solidsdraining from the main burner into the combustion zone of the auxiliaryburner.

Gases entering the bottom of the burner pass upwardly through the bodyof the vessel at a velocity regulated to maintain a dense turbulent bedof solids 56 lower portion of the burner vessel.

The coke particles are heated in the burner vessel 48 to a temperaturesubstantially above that maintained in the coking vessel. For example,the temperature of the burner vessel may be from 1000 F. to 1500 F.,usually about 200 to 300 F. above coking temperature.

The hot solids overflow from the burner vessel into a return standpipe57 and are returned to the coking vessel 7 as later described. Spentcombustion gases leaving the bed 56 to cyclone separators 58 and 59 forremoval of entrained solids are then vented to the stack through line60. Solids separated in the cyclones are returned to the bed through diplegs 61 and 62.

The standpipe 57 connects at its base with a vertically inclined conduit63 which in turn connects with a vertical riser 64 through valve 65. Acarrier gas is introduced into Jriser 64 through valved line 64 tocontrol the density in, the riser. The riser pipe 64 connects with theupper portion of the coking vessel 3 below the level of the bed. .Aportion of these hot solids may be passed through line 66 into the inletto the cyclones 13 and 14 as earlier described to supply heat and scourthe walls.

in the method of circulating the solids between the 90king vessel andthe burner vessel is substantially the same as that used to circulatethe catalyst between the reactor and regenerator in a fluid catalyticcracking unit. This method of circulation is described in greater detailin the Packie Patent 2,589,124, issued March 11, 1952, on applicationfiled May 1, 1950.

Briefly, the circulation is accomplished by maintaining. the density inthe riser pipes 47 and 64 lower than in the standpipes 43 and 57 and theconnecting fluidized beds so that the head of pressure generated at thebase of the standpipes serves as a driving force to circulate thesolids. The rate of circulation may be controlled primarily by the slidevalve 67 in riser 46 and secondarily by regulating the amount of gasentering riser 47 or 64 or both. The unit may be designed to take amaximum of about a 4 pound per square inch pressure drop through theslide valve 67'. The standpipe 57 is designed to normally maintain alevel of solids from to feet below the level of solids in the burner sothat variations in the standpipe level can compensate for pressuresurges in the system.

The rate of circulation of solids between the coking vessel and burneris controlled to supply the required heat for the process and willdepend upon the difference in temperature between the vessels. For atemperature difference of 200 F. the weight of hot solids introducedinto the coking vessel may be between about 8 to 19 times the weight ofthe oil charged per unit time.

The size of the coking vessel should be such as to give the oildistributed on the coke adequate time to be converted into vapors andcoke so that the solids passing to the burner is substantially free ofunvaporized oil. The residence time of the solids in the reactor may befrom 3 to 10 minutes or more.

The amount of coke formed in the process will be greater than thatnecessary to supply the heat for the process. This excess coke ispreferably withdrawn from the bottom of the standpipes 43 or 57. To thisend with: drawal pipes 68 and 69 connecting with conduit 70 into whichthe coke discharges into a stream of carrier gas such as steam. The cokeis carried through a conduit by means of a carrier gas such as stream toa quench zone 71. A quenching medium such as water is introduced intothe tower. The quenching medium is vaporized by heat of the solids. Thequenched solids discharge into a cyclone separator 71 where the solidsseparate from the carrier gas and vaporized quenching medium. The cokeseparated in the cyclone discharges into a standpipe 81. Air is injectedinto the standpipes at one or more points through lines 82, 83 and 84 todry strip and aerate the product coke. Standpipe 81 is sufficiently longto develop adequate pressure for subsequent pneumatic conveying of thecoke to the product storage. Flow of solids through this standpipe isregulated by slide valve 85. The coke discharges from the base of thestandpipe 85 into carrier line 86 into which carrier gas is passedthrough line 87 for transporting the coke to storage.

As before stated during the course of the operation, the individualparticles making up the fluid bed in the coking vessel grow in size dueto the deposition of coke. To maintain the desired amount of solids inthe system of the desired particle size range, it is necessary toreplace the coarser particles with finer particles. This may be done bybreaking up some of the larger particles by attrition as previouslydescribed. If desired, a part of the withdrawn coke may be ground andreturned to the system coking vessel. To reduce the amount of suchgrinding the solids withdrawn from the coking vessel and before beingdischarged from the unit or passed to the burner may be treated toselectively remove the finer par-' ticles sothat only a selected coarserfraction. is passed tothe-burner or withdrawn from the process.

This is illustrated in Figure 4 of the drawings.

To avoid duplication, only the lower portion of the coking vessel 3 andburner vessel 48 is illustrated. The upper half of the equipment is thesame as in Figures 1 and 2.

Referring to the drawing, a part or all of the solids withdrawn fromcoking vessel through standpipe 43 is passed through line 72 to theintermediate section of an enlarged elutriator vessel 73 where it iscontacted with' a rising stream of elutriating gas introduced into the'vessel below the point of entry of the SOllClS through line 74.

The velocity of the rising gas passing through the elutriating vessel 73is controlled to carry overhead a selected finer fraction of the solidswhile permitting a coarser fraction to collect in the bottom of thevessel. The elutriating gas containing the entrained fines are removedfrom the top of the vessel through line 75 and are returned to thecoking vessel preferably at a low point therein.

The elutriating vessel may be provided with a lower settling sectionbelow the point of introduction of the elutriating gas. A small amountof aerating gas may be introduced into the bottom of the elutriatorthrough line 76.

The coarse fraction is withdrawn from the elutriator 73 through conduit77. A part or all of the coarser fraction may be withdrawn as productcoke through lines 78 and 70 or a part or all may be passed through line79 for transfer to the burner.

The elutriator serves to retain the finer particles in the system untilthey have, grown to the maximum desired size for removal.

Instead of locating the elutriator as shown, it may be located at otherpoints in the system. It is generally preferred to elutriate the streambefore passing to the burner so as to pass only the coarse fraction tothe burner because the finer material burns more readily. By keeping thefiner material out of the burner, the amount of external grinding orinternal attrition can be minimized. By controlling the amount ofattrition by the high velocity stripping jets and by elutriation, theamount of fines re? tained in the system to replace the coarser materialwithdrawn can be regulated to maintain the particles at the desired sizein the system.

Returning to Figure 1, rather than withdrawing excess coke from thebottom of the standpipes 43 and 57, a part or all of the excess coke maybe withdrawn from the burner vessel through line 80 and sent to thequench tower as earlier described.

While we have described the use of high velocity steam jets in thestripping to break up coarser particles, such jets may be used in otherpoints where the solids exist in dense phase such as in the burnervessel.

The following example of a coking unit capable of processing about 3800barrels of Elk Basin petroleum residuum from vacuum distillation havinga specific gravity of 0.83 and a Conradson carbon of 30% will be helpfulto. a better understanding of the invention.

Coking vessel Dimensions:

Top straight side (disengaging zone), 9' dia. x 20' Wide diameter (belowdense bed), ll dia. x 16' .6 Middle section cone, 4' dia. x 11 dia. x34' Stripper section, 4' x 10' Amount of stripping and fluidizing steamadded at a higher point, 4940 pounds per hour Pressure of steam enteringlow pressure fluidiziug nozzles, 90 p.s.i.g.

Scrubber and fractianating tower Dimensions, 7'6" x 40' Operatingconditions:

Bottom temperature, 700 F. Trap out tray for gas oil, temperature 500 F.Top temperature, 275 F. Pressure bottom, 10 p.s.i.g. Pressure top, 9.5p.s.i.g. Temperature heavy condensate quench oil to bottom of tower, 500F., quantity 2910 b./s./d. Amount of heavy condensate recycled to coker,1290 b./s./d. Temp. of gas oil reflux to top of scrubbing zone,

500 F., quantity 1270 b./s./d. Temp. of gas oil reflux to top of tower,235 F.,

quantity 9740 b./s./d.

Burner vessel Dimensions, 11' .9" x 32' Operating conditions:

Temperature, 1125 F. Top pressure, 12 p.s.i.g. Solids hold up in burner,22 tons Air flow, 8830 standard cubic feet per minute Air blowerdischarge pressure, 32.6 p.s.i.a. Circulation rate between coking vesseland burner vessel, 4.3 tons per minute Under the above set ofconditions, the process should yield about 226 b./s./d. of naphthahaving an API gravity of 48.7, about 2320 b./s./d. of clean gas oilhaving an API gravity of 17.3, about 2.51 million standard cubic feet ofwet gas having an average molecular weight of 26.3, and about 162 tonsof excess coke per stream day.

While the coking unit forming the present invention has been describedand illustrated in simplified form, it will be understood that acomplete commercial unit will include a considerable amount ofadjunctive equipment such as pumps, valves, temperature, pressure andlevel indicators, recorders and controllers, accumulator tanks, aerationand pressure taps, emergency rundown lines, storage tanks, etc.

Having described the preferred embodiment, what is claimed is:

1. A process for the conversion of heavy oil containing metallicimpurities which deactivate cracking catalyst and are vaporizable atconversion temperatures to form a gas oil suitable for catalyticcracking and coke, which comprises introducing said oil at amultiplicity of horizontal and vertical points into the intermediatesection of an enlarged coking zone containing a body of subdivided cokeparticles, circulating a stream of coke particles from the lower portionof the coking vessel through an external heater wherein said particlesare heated by direct heat exchange and back to said coking vessel tomaintain said vessel at a temperature sufficient to convert said oilinto vapors and coke, introducing a stripping gas into the bottomsection of said vessel to remove vaporized oil from the coke passing tosaid heater, injecting stripping gas as jets ranging from 200 to 3000feet per second so as to break up large particles into small ones,maintaining said oil within said coking vessel for a period suflicientto convert said oil into vapors and coke, and passing the stripping gasand vapors formed in the process upwardly through the vessel at avelocity controlled to maintain a dense turbulent fluidized bed ofsolids in said vessel.

2. In the process for coking heavy hydrocarbon oils wherein oil feed iscontacted with a fluidized bed of particulate solids having an averageparticle size ranging between about to 500 microns in a reaction zone,said solids bed being maintained at a coking temperature by thecirculation of solids to an external heating zone, wherein the oil feedon contact with said solids bed is converted to vaporous products whichare withdrawn overhead and carbonaceous residue which deposits on saidsolids, and wherein a stripping zone is positioned below and in openfluid communication with said reaction zone, reaction zone solids beingtherein stripped of occluded hydrocarbons and passed to said heatingzone, the improvement which comprises introducing stripping gas intosaid stripping zone at jet velocities of about 200 to 3000 feet persecond so as to break up coarse particles into finer solids, the finersolids being returned to the reaction bed.

3. The improved process of claim 2 wherein said stripping gas is steam.

4. The process of claim 1 wherein the velocity of gases emerging fromsaid fluidized bed is increased to a velocity sufiicient to secureappreciable entrainment of solids from said bed by reducing the freevapor passage way of the gases whereby coking and fouling of theoverhead portions of said coking zone are substantially prevented.

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1. A PROCESS FOR THE CONVERSION OF HEAVY OIL CONTAINING METALLICIMPURITIES WHICH DEACTIVATE CRACKING CATALYST AND ARE VAPORIZABLE ATCONVERSION TEMPERATURES TO FORM A GAS OIL SUITABLE FOR CATALYTICCRACKING AND COKE, WHICH COMPRISES INTRODUCING SAID OIL AT AMULTIPLICITY OF HORIZONTAL AND VERTICAL POINTS INTO THE INTERMEDIATESECTION OF AN ENLARGED COKING ZONE CONTAINING A BODY OF SUBDIVIDED COKEPARTICLES, CIRCULATING A STREAM OF COKE PARTICLES FROM THE LOWER PORTIONOF THE COKING VESSEL THROUGH AN EXTERNAL HEATER WHEREIN SAID PARTICLESARE HEATED BY DIRECT HEAT EXCHANGE AND BACK TO SAID COKING VESSEL TOMAINTAIN SAID VESSEL AT A TEMPERATURE SUFFICIENT TO CONVERT SAID OILINTO VAPORS AND COKE, INTRODUCING A STRIPPING GAS INTO THE BOTTOMSECTION OF SAID VESSEL TO REMOVE VAPORIZED OIL FROM THE COKE PASSING TOSAID HEATER, INJECTING STRIPPING GAS AS JETS RANGING FROM 200 TO 3000FEET PER SECOND SO AS TO BREAK UP LARGE PARTICLES INTO SMALL ONES,MAINTAINING SAID OIL WITHIN SAID COKING VESSEL FOR A PERIOD SUFFICIENTTO CONVERT SAID OIL INTO VAPORS AND COKE, AND PASSING THE STRIPPING GASAND VAPORS FORMED IN THE PROCESS UPWARDLY THROUGH THE VESSEL AT AVELOCITY CONTROLLED TO MAINTAIN A DENSE TURBULENT FLUIDIZED BED OFSOLIDS IN SAID VESSEL.